1. World Data Center for Geoinformatics and Sustainable Development. Foresight COVID-19. http://wdc.org.ua/uk/covid19-project
2. Standard country or area codes for statistical use, UN Statistics Division. https://unstats.un.org/unsd/methodology/m49 /
3. COVID-19 Data Repository by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. https://github.com/CSSEGISandData/COVID-19
4. Anders Tegnell and the Swedish Covid Еxperiment, FT, SEPTEMBER 11 2020. https://www.ft.com/content/5cc92d45-fbdb-43b7-9c66-26501693a371
5. Imad Dabbura. K-means Clustering: Algorithm, Applications, Evaluation Methods, and Drawbacks. https://towardsdatascience.com/k-means-clustering-algorithm-applications-evaluation-methods-and-drawbacks-aa03e644b48a (2018)